This invention relates to a high-speed, high-force electromagnetic actuator, and particularly to an electromagnetic actuator and method for opening and closing a valve of an internal combustion engine, driving a high pressure fuel injector, or operating a high pressure fuel regulator. More particularly, this disclosure relates to an apparatus and method of dynamically measuring the inductance and rate of change of inductance of a, electromechanical actuator as the armature moves from one pole piece toward another and inferring armature position and velocity from the measured inductance. Still more particularly, this invention relates to an electronic apparatus and method of using inductance and rate of change of inductance for dynamically controlling the landing velocity of an armature in a fuel injector or an electromagnetic actuator for opening and closing a valve of an internal combustion engine.
Electromagnetic actuators, such as fuel injectors, actuators for opening and closing a valve in an internal combustion engine (hereinafter xe2x80x9cElectronic Valve Timingxe2x80x9d or xe2x80x9cEVTxe2x80x9d actuators), and fuel pressure regulators, typically include a solenoid for generating magnetic force. A solenoid is an insulated conducting wire wound to form a tight helical coil. When current passes through the wire, a magnetic field is generated within the coil in a direction parallel to the axis of the coil. The resulting magnetic field exerts a force on a moveable ferromagnetic armature located within the coil, thereby causing the armature to move from a first position to a second position in opposition to a force generated by a return spring. The force exerted on the armature is proportional to the strength of the magnetic field and the strength of the magnetic field depends on the number of turns of the coil and the amount of current passing through the coil.
While it will be appreciated by those skilled in the art of electromechanical actuators that the techniques described in the present disclosure may be applied to any electromechanical actuator, including, for example, fuel injectors or fuel pressure regulators, for purposes of clarity the present invention will be described primarily in the context of an EVT actuator for opening and closing a valve of an internal combustion engine.
An EVT actuator generally includes an electromagnet for producing an electromagnetic force on an armature. The armature is typically neutrally-biased by opposing first and second return springs and coaxially coupled with a cylinder valve stem of an engine. In operation, the armature is held by the electromagnet in a first operating position against a stator core of the actuator. By selectively de-energizing the electromagnet, the armature may begin movement towards a second operating position under the influence of a force exerted by the first return spring. Power to a coil of the actuator may then be applied to move the armature across a gap and begin compressing the second return spring.
As can be appreciated by those skilled in the art, it is desirable to closely balance the spring force on the armature with the magnetic forces acting on the armature in the region near the stator core so as to achieve a near-zero velocity xe2x80x9csoft landingxe2x80x9d of the armature against the stator core. In order to obtain a soft-landing of the armature against the stator core, power to the coil may be modulated to reduce the armature velocity as the armature approaches the stator core in the second position. The coil may then be re-energized, just before landing the armature, to draw and hold the armature against the stator core. In practice, a soft landing may be difficult to achieve because the system is continually perturbed by transient variations in friction, supply voltage, exhaust back pressure, armature center point, valve lash, engine vibration, oil viscosity, tolerance stack up, temperature, etc.
Soft landing techniques are becoming especially important with modern high-pressure fuel injectors and direct injection fuel injectors that employ strong return springs. Soft landing the injector armature reduces injector noise and internal wear. In addition to noise reduction, soft landing has the benefit of reducing power consumption in the actuator because it enables controlled metering of the coil current so as to only place the required amount of magnetic energy in the system necessary to actuate the armature. Soft landing techniques may also be applied to control the landing velocity of an armature in a high pressure fuel regulator.
In the case of EVT actuators, experimental results for particular engines and actuator arrangements indicate that to achieve quiet EVT actuator operation and prevent excessive impact wear on the armature and stator core, the landing velocity of the armature should be less than 0.04 meters per second at 600 engine rpm and less than 0.4 meters per second 6,000 engine rpm. In order to achieve these results under non-ideal conditions (e.g., the harsh environment of an internal-combustion engine), it is necessary to dynamically monitor and adjust the magnetic flux generated within the magnetic circuit to compensate for variations in operating voltage, friction within the actuator, engine back-pressure and vibration, during every stroke of the armature. External sensors, such as Hall sensors, have been used to measure flux in electromagnetic actuators. However, sensors have proven to be too costly and cumbersome for practical applications.
PID (proportional, integral, derivative) control methods have been proposed to control the landing velocity of an armature in an electromagnetic actuator. An example of using PID methods to control the landing velocity of an armature in an electromagnetic actuator is disclosed in U.S. patent application Ser. No. 09/434,513, filed Nov. 5, 1999 and entitled xe2x80x9cMethod of Compensation for Flux Control of an Electromechanical Actuator,xe2x80x9d the contents of which is hereby incorporated in its entirety into the present specification by reference. Generally, PID control systems can only perfectly compensate a linear system with state variables that are not interactive. Electromagnetic actuator systems are, however, highly nonlinear due at least in part to changing magnetic permeability as the armature moves within the actuator. In addition, the state variables of an actuator (i.e., flux, position, and velocity) are highly interactive. In order to apply PID methods to control the landing velocity of an armature in an electromagnetic actuator, simplifying linear approximations are necessary, e.g., the system must be presumed linear over small armature displacements and the state variables must be presumed to be independent. Accordingly, there is a need for a true multivariate control system capable of controlling all state variables simultaneously and compensating a nonlinear feedback control system.
The present invention overcomes the two classical limitations of pure PID control described above by providing a sensorless position estimator that enables automatic calibration of the system. Sensorless position estimation accounts for much of the non-linearity of the system. Knowing armature position throughout the armature stroke makes it possible to self-calibrate the control system. This is because once armature position is known, together with another state variable such as velocity, it is possible to employ known non-linear multivariate feedback control algorithms to control the system.
The prior art lacks a practical and cost effective method of dynamically measuring armature position during the armature stroke. While lasers have been used in laboratory settings to measure armature position, it is not practical or cost effective to put a laser on actuators manufactured for large-scale production. Other more cost-effective methods of position sensing have not proven to be accurate and durable enough. For example, in automotive applications, position sensors must be able to withstand the temperature and vibration extremes of being mounted on an engine. Sensor-based techniques also present the problem of cabling the signal through a potentially electrically noisy environment. Accordingly, there is a need to estimate armature position in a sensorless manner.
Thus, a need exists for a sensorless self-calibrating control system and method for an electromagnetic actuator capable of dynamically compensating for non-ideal disturbances that exist in and near internal combustion engines. Further, a need exists for a high-speed sensorless control system and method for an electromagnetic actuator capable of detecting and compensating for the above-described non-ideal conditions during each stroke cycle of the armature.
A sensorless method of controlling the landing velocity of an armature in an electromagnetic actuator is provided. The method disclosed dynamically measures actuator inductance and rate of change of inductance as the armature moves within the coil. The B-H magnetization characteristics of the actuator during an armature stroke are determined during actuator operation and the measured inductance and rate of change of inductance are thereby compensated for non-linear permeability and magnetization effects. The measured inductance may be normalized at zero gap. In a preferred embodiment, the normalization at zero gap is to unity (1.0). From inductance, an estimation of position is made; from rate of change of inductance, armature velocity information is inferred. The armature position and rate information are provided to a control system for modulating a current delivered to the actuator, thereby controlling the armature landing velocity.